Particle therapy systems use an accelerator to generate a particle beam for treating afflictions, such as tumors. In operation, particles are accelerated in orbits inside a cavity in the presence of a magnetic field, and are removed from the cavity through an extraction channel. A magnetic field regenerator generates a magnetic field bump near the outside of the cavity to distort the pitch and angle of some orbits so that they precess towards, and eventually into, the extraction channel. A beam, comprised of the particles, exits the extraction channel.
A scanning system is down-beam of the extraction channel. In this context, “down-beam” means closer to an irradiation target (here, relative to the extraction channel). The scanning system moves the beam across at least part of the irradiation target to expose various parts of the irradiation target to the beam. For example, to treat a tumor, the particle beam may be “scanned” over different cross-sections of the tumor. An energy degrader changes the energy of the particle beam to reach the different cross-sections of the tumor.